Chunk by is easier to understand by example, so here goes:
If you specify:
From: 1
To: 100
Chunk by: 25
DrawMerge will generate numbers like this:
1
26
51
76
2
27
52
77
...
25
50
75
100
In other words, it divides the numbers up into four chunks and "interleaves" them. This can be quite useful, when printing multi-pat forms, for example.
DrawMerge insists on chunk-by values that make sense. For example, the total quantity of numbers you want to generate must be evenly divisible by the chunk value. If not, DrawMerge will warn you.
See DrawMerge displays a warning message when I ... for more information.